1. Field of the Invention
This invention relates generally to a multi-pad, multi-function electrode, and more specifically, to an electrode having multiple conductive polymer pads which enable a single set of electrodes to perform multiple electrical, physiological functions with respect to a patient, such as monitoring and stimulating of the patient's heart, at or about the same time.
2. Background Information
Prior art electrodes have traditionally been single-function electrodes which can be divided into two classes according to their function, whether monitoring or stimulation. A monitoring electrode is used to transfer electrical impulses from a patient's body to a cardiac system which usually displays the impulses to permit monitoring of that patient's heart condition; a stimulating electrode, on the other hand, is used to deliver stimulating electrical impulses from a cardiac system to a patient's body to permit either defibrillation or external pacing of that patient's heart.
The prior art monitoring and stimulating electrodes differ quite a bit in their physical characteristics. The monitoring electrode, for example, is typically 2-4 cm. in diameter with a single 1-2 cm. conductive center pad for receiving electrical impulses from a patient's heart, and delivering them to a monitor. The stimulating electrode, on the other hand, at least a stimulating electrode for delivering high energy to a patient for either defibrillation or external cardiac pacing, is typically 10-14 cm. in diameter with a single 8- cm. conductive center pad for delivering electrical impulses to a patient's heart from a voltage or current generator of a cardiac system.
The majority of prior art electrodes, whether for stimulating or monitoring, are constructed similarly. They are made of a flexible foam backing attached to a piece of metal foil with a connecting lead attached to the center. The foil in turn is attached to a conductive gel-filled sponge which is surrounded by a ring of flexible adhesive foam for attachment to a patient's skin.
These prior art electrodes suffer from a number of problems. First, they are severely limited in their ability to perform multiple electrical, physiological functions with respect to a patient from a single set of electrodes. As a result, it is necessary to either perform multiple electrical, physiological functions sequentially from a single set of electrodes, or else use multiple sets of electrodes simultaneously, in order to deliver multiple electrical, physiological functions to a patient. Each one of these approaches has an associated set of problems.
Sequential defibrillating and monitoring from a single set of prior art electrodes, although possible, will in many cases necessitate a long wait between the performance of the monitoring and defibrillating functions until the electrodes have depolarized, i.e. discharge stored energy (see ensuing discussion). This will in many instances result in delays in delivering necessary care to a patient under emergency conditions, which can have disastrous consequences.
Also, sequential pacing and monitoring from a single set of electrodes will simply be impossible since a pacing pulse must be administered at least sixty times per minute, and there will be insufficient time between the application of the pacing pulses for the electrodes to depolarize, i.e., discharge energy from the pacing pulses which has been stored in the electrodes through a process called polarization. Since there may be insufficient time for the electrodes to depolarize, i.e. discharge the stored energy, before the electrodes are used to monitor, the stored energy will mask the electrical impulses being received from the patient's heart, and accurate monitoring will be impossible.
The theoretical basis for how an electrode stores energy is that the electrode effectively forms a capacitor, with the metal foil forming one plate of the "capacitor," the internal "wet" portion of the body forming the second plate, and the conductive pad (typically a gel-filled sponge) comprising the material placed between the "capacitor" plates. When the electrode is used to stimulate a patient's heart, and a current pulse is delivered through the electrode to effectuate either pacing or defibrillation, the voltage between the "capacitor" plates builds up slowly, typically to levels of several hundred millivolts. The voltage takes time to build up as the material between the "capacitor" plates, i.e. the conductive pad, polarizes in order to store charge.
However, once the sponge-filled gel is polarized, it will take time to depolarize. Therefore, long after the current pulse has been applied, the "capacitor" will still retain a voltage of several hundred millivolts until the conductive pad depolarizes, and the "capacitor" discharges. Since effective monitoring must be sensitive enough to pick up a signal on the order of one millivolt from a patient's body, the continued storage of charge, resulting in a voltage of several hundred millivolts remaining across the "capacitor" plates, may drown out the signal from the patient's body, making stimulation and monitoring from the same electrode, difficult, if not impossible, until the electrode depolarizes.
A problem with using multiple sets of electrodes is that it is cumbersome and unwieldy since the wires from the many sets often become twisted. The twisting of the wires is problematic since it may result in delays in delivering necessary emergency care to a patient.
Another problem is that the multiple sets of electrodes will move, and it will be difficult to ensure consistent placement of the electrodes with respect to one another. Without consistent placement of the monitoring electrodes, the visual display of a patient's heart condition may be heavily biased since it is heavily dependent on the placement of the monitoring electrode with respect to the stimulating electrode.
Prior art electrodes also suffer from problems unrelated to sequential or multiple use. For example, prior art electrodes do not typically adhere properly to a patient's skin since only a small portion of the surface area of the electrode, the ring of flexible adhesive attached to the gel-filled foam, is available for adhering to the patient's skin. As a result, the electrode will typically adhere poorly, causing the defibrillating or pacing electrical impulses to pass through the skin in the few places where contact has actually been made, leading to skin burns. Also, these electrodes may tend to move, and any movement of the monitoring electrode while monitoring is being performed will interfere with and alter the electrical impulses being received from the patient's body by introducing biases known as monitoring artifacts, which will in turn lead to inaccurate diagnosis and monitoring of the patient's heart condition. Moreover, the conducting pad in the prior art electrodes is typically a saline-based, gel-filled sponge, and movement of the electrode will cause the gel to smear over the surface of a patient's chest. The smearing of the gel further limits the ability of a single set of prior art electrodes to perform multiple electrical, physiological functions, since the smearing of the conductive gel will result in an electrical interaction between the electrical impulses being delivered and received from a patient's heart in support of the stimulation and monitoring functions. Also, besides smearing, the prior art gels will leave a residue on the patient's skin, and they may take a long time to depolarize which further limits the ability of a single set of prior art electrodes to perform multiple electrical, physiological functions.
Accordingly, it is an object of the present invention to provide an electrode having multiple conductive polymer pads which enable a single set of electrodes to perform multiple electrical, physiological functions at or about the same time, such as stimulating and monitoring of a patient's heart.